Scaling +and positioning of controls

Interface elements +a user has to select and manipulate should not be smaller than the smallest +average finger pad, that is, no smaller than 1 cm (0.4") in diameter or a +1 cm × 1 cm square.

In the Symbian platform, UI style defines the minimum +sizes for a UI element considered as finger usable:

7 x 7 mm with 1 mm gaps for index finger usage
8 x 8 mm with 2 mm gaps for thumb usage
List type of components should have minimum of 5 mm line spacing

The width of a finger limits the density of items on screen. If the +items are too close, the user will not be able to choose a single one.

As +the probability of the user touching the higher end of the button (than on +the either side of the key) is high, button and icon sizes can be increased +vertically.

Essential information or features, such as a label, instructions, +or sub-controls should never be placed below an interface element that can +be touched, as it may be hidden by the user's finger.

+ +Following are some useful tips that can be used while placing essential +information or features on interface element:

With interfaces having input devices, it makes sense to place targets +like menu items on the edges of screens because the cursor movement stops +at the edge of the screen.
When using a touch screen, a user seldom drags the finger across the +screen like a cursor. Instead, they most likely lift their finger and place +it on a new target. Users may have difficulties in reaching the objects located +on the edges of the screen, especially if the physical device has protruding +edges around the touch screen panel. Additionally, with some devices, the +screen edges may be less sensitive to register the touch input.